Sealing body for well perforation operations

ABSTRACT

A sealing body is provided for use in well operations such as oil/gas well perforation operations. The sealing body comprises a shell defining a closed cavity; the shell is comprised of a metal alloy. The sealing body has neutral or positive buoyancy. In one embodiment, the sealing body further comprises a reinforcement structure in the cavity. The reinforcement structure may comprise one or more pairs of ribs adjoining an inner surface of the shell of the sealing body.

RELATED APPLICATION

This application claims the benefit under Title 35, U.S.C., S.199(e) ofCanadian Application No. 2,752,864 filed on Sep. 21, 2011, which isherein incorporated by reference.

TECHNICAL FIELD

The present invention relates to a sealing body for use in a perforatinggun for well perforation operations such as oil/gas well perforationoperations.

BACKGROUND

Contemporary well drilling operations in the oil and gas industry mayemploy a specialized completion operation that facilitates the flow offluids and gasses from a producing geological formation into a wellbore. Typically, this operation involves the insertion of a metaltubular casing into a bare well bore, down to the full depth of thedrilled hole. This casing strengthens the bore wall, ensures that no oilor natural gas seeps out of the well hole as it is brought to thesurface and keeps other fluids or gases from seeping into the formationthrough the well. With the metal casing in place, a cement mixture maybe pumped down-hole for added protection and structural integrity of thewell. This mixture fills the annular space formed between the casingoutside diameter and well bore and is left for a period of time toharden. Before hardening takes place, any cement remnants within thecasing must be cleared so that the internal production passage isunobstructed. After the cement hardens in the annular space, a“composite” cement and metal bore wall is formed, and the completed wallis ready for perforation operations.

The composite wall section of the well bore is perforated or pierced topermit the passage of liquid and/or gaseous hydrocarbons into the well.A tool called a perforating gun may be used to create an array ofperforations at various predetermined locations in the well. Theperforating gun typically is assembled with a plurality of directionallyshaped charges, aligned in such a way that at least one side of thecasing is completely penetrated upon firing of the gun. The holepenetrations are formed by vaporizing local casing material by one ormore jets of intense heat and pressure emitted by the gun. The jetcontinues for some distance beyond the composite wall. Depending on thetype of formation and strength of the charge, this distance may betwelve inches or more.

The perforating gun is triggered at one or more predetermined locationsin the well bore by various techniques. One type of perforating gun usesa pressurized triggering technique with pressure zones defined by seatsplaced at predetermined locations within the tubular casing of the well.The seats receive sealing bodies of varying sizes corresponding orcomplementary to the seat. A sealing body is pumped down-hole to thecorresponding seat and the well bore pressure above the seat isincreased until a predetermined pressure threshold is met or exceeded inthe pressure zone, causing the perforating gun to be activated and fire

The sealing bodies that are used in a perforating gun must be capable ofwithstanding the high pressures needed to trigger the gun and may bebuoyant in order to be easily recoverable from the well. Sealing bodiesused in perforating guns typically are spherical in shape and composedof a polymeric solid such as BAKELITE, Garolite G10, PEEK or TORLON. Thespecific gravities of these polymeric bodies are generally in the rangeof 1.3 to 1.5 relative to water which makes them negatively buoyant andless likely to be recovered by back-flowing the well, particularly ifthere is insufficient well flow to push the polymer sealing body back tothe surface of the well.

Sealing bodies comprised of polymeric solids are prone to breakage andfailure during the pressurization of the perforating gun. If the sealingbody is damaged or breaks during use, zone pressure needed to triggerthe perforating gun is lost and the process must be repeated with a newsealing body. The failed sealing body may need to be drilled out of theseat. Failure of the polymeric sealing body often occurs when thesealing body shears off at the seat contact line, with the lower portionof the sealing body being lost down hole. If a sealing body is recoveredafter the perforating gun fires, the sealing body may be broken ordamaged, or stressed at the point of contact between the sealing bodyand the seat and thus the sealing body cannot be reused. Because ofthese characteristics, sealing bodies comprised of polymeric solidstypically are not re-used for multiple perforation operations.

SUMMARY

Embodiments of the present invention provide a sealing body for use inwell perforation operations. The sealing body comprises a shell defininga closed cavity, wherein the shell is comprised of a metal alloy; andwherein specific gravity of the sealing body is less than or equal to 1,where 1 is the specific gravity of water. In one embodiment, the shellis comprised of a titanium alloy, such as Ti-6Al-4V. In one embodiment,the sealing body further comprises a reinforcement structure in thecavity. The reinforcement structure may comprise one or more pairs ofribs adjoining an inner surface of the shell of the sealing body.

According to another embodiment of the present invention there isprovided a method of performing well perforation operations. The methodcomprises introducing a sealing body into a seat positioned in a wellbore, the sealing body comprising a shell defining a closed cavity,wherein the shell is comprised of a metal alloy; and wherein specificgravity of the sealing body is less than or equal to 1, where 1 is thespecific gravity of water; and pressurizing a portion of the well boreup-hole from the seat to a predetermined pressure threshold fortriggering a perforating gun.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a cross section view of a well bore; FIG. 1 b is a enlargedview of a portion of the cross-section of FIG. 1 a;

FIG. 2 is a close-up view of an embodiment of a sealing body seated in aball seat;

FIG. 3 a is a front view of an embodiment of a sealing body, FIG. 3 b isa perspective cutaway view of the sealing body and FIG. 3 c is a crosssection of the sealing body;

FIG. 4 a is a transparent isometric view an embodiment of a sealingbody, FIG. 4 b is a perspective cutaway view of the sealing body, FIG. 4c is a side view of the sealing body, FIG. 4 d is a cross-section viewof FIG. 4 c along the line A-A, FIG. 4 e is a side view of the sealingbody, FIG. 4 f is a cross-section view of FIG. 4 e along the line B-B;

FIG. 5 a is a transparent isometric view an embodiment of a sealingbody, FIG. 5 b is a perspective cutaway view of the sealing body, FIG. 5c is a side view of the sealing body, FIG. 5 d is a cross-section viewof FIG. 5 c along the line A-A, FIG. 5 e is a side view of the sealingbody, FIG. 5 f is a cross-section view of FIG. 5 e along the line B-B;and

FIG. 6 a is a transparent isometric view an embodiment of a sealingbody, FIG. 6 b is a perspective cutaway view of the sealing body, FIG. 6c is a side view of the sealing body, FIG. 6 d is a cross-section viewof FIG. 6 c along the line A-A, FIG. 6 e is a side view of the sealingbody, FIG. 6 f is a cross-section view of FIG. 6 e along the line B-B.

Like reference numerals are used in the drawings to denote like elementsand features.

While the invention will be described in conjunction with theillustrated embodiments, it will be understood that it is not intendedto limit the invention to such embodiments. On the contrary, it isintended to cover all alternatives, modifications and equivalents as maybe included within the spirit and scope of the invention as defined bythe appended claims.

DETAILED DESCRIPTION OF EXAMPLE IMPLEMENTATIONS

FIGS. 1 a and 1 b illustrate high level views of a well 10, a wellborecasing 12 and perforation gun system 14. The perforation gun system 14,a portion of which is shown in FIGS. 1 a and 1 b, is used to perforatepredetermined sections of the wellbore casing 12 to permit the passageof liquid and/or gaseous hydrocarbons into the well 10. The perforationgun system 14 comprises one or more perforating guns 16 a, 16 b, 16 c.The perforating guns 16 a, 16 b, 16 c are fired at planned locationswithin a number of pressure activation zones 18 a, 18 b, 18 c in thewell 10. A sequence of perforation operations may be performed typicallystarting with triggering the perforating gun 16 a furthest down-hole,then the next perforating gun 16 b down-hole and so forth, in order toperforate the wellbore casing 12.

Triggering the perforating gun 16 may be accomplished by a number ofmeans. One method involves the use of a pressurized triggeringtechnique, within a pressure activation zone 18 defined by a seat 20installed at a pre-determined location within the wellbore casing 12down-hole from the corresponding perforating gun 16. When pressure inthe activation zone 18 surrounding the perforating gun 16 reaches apre-set level, an internal mechanism (not shown) in the perforating gun16 is activated and the perforating gun 16 fires a plurality of shapedcharges through the wellbore casing 12 and into the geological formationsurrounding the well 10. Each pressure activation zone 18 coincides witha geological formation planned for perforation and spans the up-hole anddown-hole sides of a perforating gun location. The perforating gunposition is carefully chosen to intersect with the geological productionzone.

The seat 20 receives a sealing body 24 that corresponds or iscomplementary to the seat 20. The seat 20 receives the sealing body 24in order to form a temporary tight pressure seal and define the pressureactivation zone 18 in the well 10. The perforating gun system 14includes multiple seats 20 a, 20 b, 20 c situated down-hole of theperforating guns 16 a, 16 b, 16 c.

In one embodiment, the sealing body 24 is generally spherical and may beused with existing perforating guns 16 and seats 20, such as a ball seat26 illustrated in FIG. 2. The ball seat 26 has a conical face 28 forreceiving a corresponding generally spherical sealing body 24. In otherembodiments, the sealing body 24 may be oval, oblong or generallyegg-shaped or bullet-shaped. In some embodiments the sealing body 24 hasa biased weight distribution in order to ensure the sealing body 24 isoriented to contact the seat 20 and create a tight pressure seal withthe seat 20 after the sealing body 24 is introduced into the well 10.Embodiments of a sealing body 24 according to the present disclosure aredescribed in greater detail below.

The operation of the seat 20 and activation of the perforating gun 16will be described with respect to the seat 20 b and perforating gun 16 billustrated in FIG. 1 b. A sealing body 24 b is dropped or pumped withfluids down the well 10 to the corresponding seat 20 b. In someembodiments, the sealing body 24 b is neutral or slightly buoyant in thewell fluids and thus is pumped down-hole to the corresponding seat 20 b.The sealing body 24 b is sized to pass through the up-hole seat 20 c andto mate and form a tight pressure seal with seat 20 b. In oneembodiment, the sealing body 24 b mates and forms a seal with the seat20 b in any orientation of the sealing body 24 b. Using high pressurepumps on the drilling rig (not shown) the well bore pressure above theseat 20 b and sealing body 24 b is increased until a predeterminedpressure threshold is met or exceeded in the pressure activation zone 18b, causing the perforating gun 16 b to be activated and fire. After theperforating gun 16 b fires, the sealing body 24 b floats and/or travelswith the fluids in the well 10 to the top of the well 10 to be recoveredat the wellhead (not shown).

If there is more than one zone to produce, a number of perforationoperations are carried out. The smallest sized sealing body 24 a ispumped down the well 10 and travels through seats 20 b, 20 c to the seat20 a in order to create a high pressure in the activation zone 18 a totrigger the perforating gun 16 a furthest down the well 10. After theperforating gun 16 a fires, the sealing body 24 a floats and/or travelsto the top of the well 10 and is recovered. Then, a larger sized sealingbody 24 b is pumped down the well 10 and travels through seat 20 c tothe seat 20 b in order to create a high pressure in the activation zone18 b to trigger the perforating gun 16 b at the next predeterminedlocation furthest down the well. The larger sealing body 24 b similarlyis recovered before activating the next perforating gun 16 c. A sealingbody 24 c, larger than sealing body 24 b, is pumped down the well 10 andtravels to the seat 20 c to create high pressure in the activation zone18 c to trigger the last perforating gun 16 c. It will be appreciatedthat each perforated zone may be fractured using specialized chemicalsin conjunction with high pressure pumping, prior to introducing the nextsealing body 24 in preparation for a perforation operation.

Thus, sealing bodies 24 a, 24 b, 24 c of varying sizes are provided tomate and form a seal with seats 20 a, 20 b, 20 c. The sealing body 24that is used with the seat 20 is capable of withstanding the highpressures needed to trigger the perforating gun 16, typically above10,000 psi. Down-hole pressure loads may act uniformly or asymmetricallyaround the sealing body 24. The sealing body 24 is subject to uniformpressure as it is being pumped down-hole to the seat 20. The sealingbody 24 experiences asymmetric loading when landed in the seat 20 duringpressure-up operations for triggering the perforating gun 16. The forceasymmetry arises from the leak-tight barrier formed between the sealingbody 24 and seat 20, whereby the pressure imbalance acts to attempt topush the sealing body 24 through the seat 20. The sealing body 24 alsois subject to local stresses at the point of contact between the sealingbody 24 and the seat 20. For example, in the embodiment illustrated inFIG. 2, severe localized stress may occur in the sealing body 24 if onlyline contact is made with the internal frustum of the conical ball seat26.

The sealing body 24 also preferably has a specific gravity of less thanor equal to 1, where 1 is the specific gravity of water, and thuspositive or neutral buoyancy to aid the recovery of the sealing body 24after the perforating gun 16 is fired. Fluids used for wellborefracturing and perforation operations generally have a higher specificgravity than water, ranging from 1.02 to 1.40 or higher. The sealingbody 24, with a lower specific gravity, is pumped down the well 10 tothe corresponding seat 20 and during recovery, floats to more easilytravel to the top of the well 10 for recovery. The sealing body 24typically is recovered at the surface with the fracturing fluid, or withwater which may be located near the wellbore, ahead of the producedpetroleum products. The sealing body 24 also may be recovered along withproduced petroleum products. Although produced petroleum productstypically are lighter and may have specific gravities of less than 1,the sealing body 24, with a specific gravity of less than or equal to 1,may be recovered with the flow of the produced petroleum products.

FIGS. 3 a, 3 b, 3 c through FIGS. 6 a to 6 f illustrate a sealing body24 according to embodiments of the present invention. In one embodiment,the sealing body 24 comprises a shell defining a closed or sealedcavity. The cavity is closed or sealed to provide a hollow sealing body24 with positive or neutral buoyancy. The sealing body 24 is comprisedof a metal alloy to provide strength to withstand down-hole pressures inthe well during well perforation operations. The sealing body 24 issized with a shell thickness to provide strength and at the same timemaintain a mass to volume ratio such that the specific gravity of thesealing body 24 is less than or equal to 1, where 1 is the specificgravity of water, in order to provide a sealing body 24 with positive orneutral buoyancy.

In one embodiment, the sealing body 24, as illustrated in FIGS. 3 a, 3 band 3 c comprises a shell 52 which is generally spherical in shape anddefines a closed or sealed cavity 54. The cavity 54 is closed or sealedto provide a hollow sealing body 24 with positive or neutral buoyancy.The shell 52 is comprised of a metal alloy in some embodiments. Thethickness of the shell 52, between an inner surface 56 and a finishedouter surface 58, is configured based on the size of the sealing body 24and density of the metal alloy in order to provide strength and alsomaintain a mass to volume ratio resulting in a specific gravity of lessthan or equal to 1. In one embodiment, the outer diameter of the shell52 is defined in relation to the thickness of the shell 52 in accordancewith the formula:

${27.7008 \times \left( \rho_{metal} \right) \times \frac{\left( {1 - d^{3}} \right)}{D^{3}}} \leq 1$

where:

-   -   ρ_(metal)=density of the shell material (lbs/in³);    -   D=outer sphere diameter (inches);    -   d=inner sphere diameter (inches);    -   27.7008=a specific volume constant for water (equal to the        inverse of the density of pure water, 0.0361 lb/in³); and    -   1=the numerical equivalent of specific gravity.        A metric equivalent is provided by the formula:

${\left( \rho_{metal} \right) \times \frac{\left( {1 - d^{3}} \right)}{D^{3}}} \leq 1$

In one embodiment, the sealing body 24 may be used with a seat 20comprising a ball seat 26, as illustrated in FIG. 2. The sealing body 24mates with the ball seat 26 which has a conical face 28 which acts as areceiving surface for the sealing body 24. A tight pressure seal isformed between the sealing body 24 and the conical face 28.

As described above, the sealing body 24 is sized with a shell thicknessto provide strength to withstand downhole pressures, asymmetric pressureloads and stresses from the contact of the sealing body 24 and the seat20 or the ball seat 26. The loads and stresses on the sealing body 24may depend on the geometry and design of the seat 20 or ball seat 26.For example, for the ball seat 26, the asymmetric loading and contactstresses experienced by the sealing body 24 vary with the angle of theconical face 28 of the ball seat 26. This angle affects the magnitude ofthe load on the line of contact proportional to (Cos φ)⁻¹, where φrepresents the angle of the conical face 28 relative to the longitudinalaxis 30 of the well 10. As the ball seat 26 becomes shallower andapproaches shape of a cylinder, contact stresses near infinity and linecontact with the sealing body 24 occurs on increasing diameters or outerdimensions of the sealing body 24.

The sealing body 24 may have slight irregularities in the shape and theouter surface 58 of the spherical shell 52. In use, once the sealingbody 24 is seated in the ball seat 26 and pressure in the pressureactivation zone 18 increases, a seal will still form as the sealing body24 starts to deform under pressure loads and the pressure imbalance actsto attempt to push the sealing body 24 through the ball seat 26. In oneembodiment, the spherical shell 52 has a surface variance of not morethan +/−0.01 inches in order to form a tight seal with the ball seat 26.

The sealing body 24 is comprised of a metal alloy with suitable strengthand density properties, such as a high strength material having a lowdensity. Suitable light metal alloys include titanium alloy or alloys ofaluminum, magnesium and beryllium. In one embodiment, the metal alloycomprises a Ti-6Al-4V titanium alloy. The Ti-6Al-4V titanium alloy has ayield strength of 128,000 psi, and 2) density of 0.168 lbs/in³ and iscomposed of the following elements by percent weight; 1) aluminum 6%, 2)iron 0.25% (maximum), 3) oxygen 0.2% (maximum), 4) vanadium 4%, and 5)titanium—balance (90%). Other grades of titanium are available withsimilar characteristics, and therefore the material of the sealing body24 is not limited to grade Ti-6Al-4V.

In one embodiment, the sealing body 24 further comprises an internalreinforcement structure 60. The internal reinforcement structure 60provides strength for the sealing body 24 to withstand pressures andloading during use, including asymmetric loading and localized stressesexperienced by the sealing body 24 when mated with the seat 20. For asmaller sized sealing body 24, the thickness of the shell 52 may belimited in order to ensure the specific gravity of the sealing body 24is less than or equal to 1 and the internal reinforcement structure 60provides additional strength to compensate for a thinner shell 52. Areinforcement structure 60 may be included in a sealing body 24 in orderfor the sealing body 24 to withstand increased stresses related to thegeometry of the seat 20, such as for a ball seat 26 with a shallow angleof its conical face. The reinforcement structure 60 adds weight to thesealing body 24 and thus it is configured along with the thickness ofthe shell 52 based on the outer diameter of the sealing body 24 and thedensity of the metal alloy in order to provide a sealing body 24 withsufficient strength and at the same time maintain a mass to volume ratioresulting in a specific gravity of less than or equal to 1.

In one embodiment, during use, the sealing body 24 is pumped down thewell 10 and comes to rest in the seat 20 in a randomly determinedorientation and thus the reinforcement structure 60 is configured to beeffective and provide strength to the sealing body 24 in anyorientation.

Example embodiments of a sealing body 24 with an internal reinforcementstructure 60 are illustrated in FIGS. 4 a to 4 f through 6 a to 6 f. Inone embodiment, the reinforcement structure comprises one or more pairsof ribs 70, 72. In some embodiments, the ribs 70, 72 comprise circularbands adjoining the inner surface 56 of the shell 52 of the sealing body24. The ribs 70, 72 project from the inner surface 56 of the shell 52towards a center of the sealing body 24. In one embodiment, the one ormore pairs of ribs 70, 72 are spaced evenly within the shell 52 andsymmetrically within two half sections of the sealing body 24. The planeof the circle of each rib 70 may be orthogonal to the plane of thecircle of the other rib 72 in the pair of ribs. The ribs 70, 72 increasethe ability of the sealing body 24 to resist pressures in the well 10,including asymmetric pressure loading from zone pressurizationoperations used to trigger a perforation gun 16. Other configurations ofreinforcement structures are contemplated.

As can be seen, for example, in FIGS. 4 a to 4 f, in one embodiment, theribs 70, 72 have a generally square cross-section with a width of 2.0mm, or approximately 0.079 inches, and a height, from the inner surfaceof the shell 52, of 2.0 mm, or approximately 0.079 inches. Outer edgesof the ribs 70, 82 may be slightly rounded. Fillet edges with a radiusof 0.02 inches may be formed where the ribs 70, 72 adjoin the innersurface 56 of the shell 52. In other embodiments, the ribs 70, 72 have agenerally rectangular cross section or a generally semi-circular crosssection.

The one or more pairs of ribs 70, 72 are comprised of a metal alloy withsuitable strength and density properties, such as a high strengthmaterial having a low density. Suitable light metal alloys includetitanium alloy or alloys of aluminum, magnesium and beryllium. In oneembodiment, the metal alloy comprises a Ti-6Al-4V titanium alloy. TheTi-6Al-4V titanium alloy has a yield strength of 128,000 psi, and 2)density of 0.168 lbs/in³ and is composed of the following elements bypercent weight; 1) aluminum 6%, 2) iron 0.25% (maximum), 3) oxygen 0.2%(maximum), 4) vanadium 4%, and 5) titanium—balance (90%). Other gradesof titanium are available with similar characteristics, and thereforethe material of the ribs 70, 72 is not limited to grade Ti-6Al-4V. Inone embodiment, the ribs 70, 72 are comprised of the same metal alloy asthe shell 52.

In the embodiment illustrated in FIGS. 4 a to 4 f, the internalreinforcement structure comprises one pair of ribs, 70, 72 in thesealing body 24. The ribs 70, 72 are positioned such that the planes ofthe circular ribs are orthogonal and each plane intersects a centre ofthe sealing body 24. The ribs 70, 72 intersect at two points on theinner surface 56 of the shell 52.

In the embodiment illustrated in FIGS. 5 a to 5 f, the internalreinforcement structure comprises two pairs of ribs, 80, 82 and 84, 86.The ribs 80, 82 and 84, 86 are spaced evenly and orthogonally within thesealing body 24. In the orientation shown in FIG. 5 a, one of each pairof ribs, 80, 84 is shown extending vertically around the inner surface56 of the sealing body 24 and the other of each pair of ribs, 82, 86 isshown extending horizontally around the inner surface 56 of the sealingbody 24. In one embodiment the ribs 80, 82 and 84, 86 are offset anequal distance from a center of the sealing body 24. In an embodiment ofa sealing body 24 comprised of Ti-6Al-4V titanium alloy and having anouter diameter of 1.75″, the ribs are spaced 0.613 inches apart, asmeasured between the outer surfaces of the ribs.

In the embodiment illustrated in FIGS. 6 a to 6 f, the internalreinforcement structure comprises three pair of ribs 90, 92, 94, 96 and98, 100. The ribs 90, 92, 94, 96 and 98, 100 are spaced evenly andorthogonally within the sealing body 24. In the orientation shown inFIG. 6 a, one of each pair of ribs, 90, 94, 98 is shown extendingvertically around the inner surface 56 of the sealing body 24 and theother of each pair of ribs 92, 96, 100 is shown extending horizontallyaround the inner surface 56 of the sealing body 24. In the embodimentillustrated, one pair of ribs 94, 96 is positioned such that the planesof the circular ribs 94, 96 intersects a centre of the sealing body 24and two of the pairs the ribs 90, 92 and 98, 100 are offset an equaldistance from a center of the sealing body 24. In an embodiment of asealing body 24 comprised of Ti-6Al-4V titanium alloy and having anouter diameter of 2.0″, the ribs 90, 92, 94, 96, 98, 100 are spaced0.391 inches apart, as measured between the outer surfaces of the ribs.

Sealing bodies 24 according to the present disclosure may be provided indiscrete sizes for use in a sequence of perforating operations asdescribed above. In example discrete sizes of a sealing body 24 having agenerally spherical shell 52 comprised of Ti-6Al-4V titanium alloy, thesealing body 24 has an outside diameter in a range of 1.25 to 3.5 inchesand the shell 52 has a thickness, between the inner surface 56 and theouter surface 58 in a range of 0.042 to 0.135 inches. Specifications ofexample sizes of sealing bodies 24 comprised of Ti-6Al-4V titanium alloyare listed in Table 1 below. Size increments of ¼″ are used in theexamples in Table 1 in order to provide a series of sealing bodies 24for use in multi-zone perforation operation. Other fractional sizeincrements and size ranges may be used. A positive buoyancy rating inTable 1 refers to a sealing body 24 with a specific gravity of less than1 and a neutral buoyancy rating refers to a sealing body 24 with aspecific gravity equal to 1. In the example embodiments described inTable 1 for Ti-6Al-4V titanium alloy, an internal reinforcementstructure 60 comprising one or more pairs of ribs 70, 72, is includedfor a sealing body 24 with an outer diameter (OD) in the range of 1.25to 2.0 inches.

TABLE 1 Example Sealing Body Specifications Estimated Sealing SphericalEquivalent Sealing Shell Spacing Body OD Volume H2O Weight Body Weightthickness No. of between Bouyancy (in) (in³) (Pure) (lbs) (lbs) (in)Ribs ribs Rating 1.25 1.023 0.037 0.037 0.042 2 — Neutral 1.50 1.7670.064 0.064 0.055 2 — Neutral 1.75 2.806 0.101 0.101 0.055 4 0.613Neutral 2.0 4.189 0.151 0.151 0.06 6 0.391 Neutral 2.25 5.964 0.2150.210 0.085 0 n/a Positive 2.50 8.181 0.295 0.290 0.095 0 n/a Positive2.75 10.889 0.393 0.388 0.105 0 n/a Positive 3.00 14.137 0.510 0.5050.115 0 n/a Positive 3.25 17.974 0.649 0.645 0.125 0 n/a Positive 3.5022.449 0.810 0.807 0.135 0 n/a Positive

The OD, shell thickness and presence and configuration of an internalreinforcement structure 60 in the sealing body 24 will vary fordifferent metal alloys or different titanium alloys. Further, dependingon the environment, pressures and loading the sealing body 24 is exposedto during use, smaller sizes of sealing bodies 24 may be providedwithout an internal reinforcement structure 60. Similarly, larger sizesof sealing bodies 24 may be configured to include an internalreinforcement structure 60 to increase the strength of the sealing body24.

The cavity 54 of the sealing body 24 may be substantially empty andfilled with air captured within the cavity 54 as the sealing body 24 ismanufactured. In one embodiment, the cavity 54 of the sealing body 24comprises a vacuum to provide a slight increase in buoyancy of thesealing body 24. In another embodiment, the cavity 54 of the sealingbody 24 is filled with liquid or gas to increase the strength of thesealing body 24. Light gases or petroleum distillates with specificgravities much less than 1.0, such as specific gravities around 0.01 to0.25, may be used as a filling media to increase the strength of thesealing body 24 while maintaining a neutral or positive buoyancy. In oneembodiment, the cavity 54 is filled with frozen CO2 or “dry ice” priorto joining the two halves of the sealing body 24. The dry ice sublimatesto gas as it warms up and creates pressure within the cavity 54 toincrease the strength of the sealing body 24.

Sealing bodies 24 according to the present disclosures may bemanufactured in two halves and joined at an equatorial seam. The halvesmay be geometrically equivalent and can be produced from the same mold.Different mold types, such as press molds or sand casting type molds maybe used to create the halves of the sealing body 24. The molds aredesigned to receive a molten charge of metal alloy, such as titaniumalloy, for sand molds or a near-melted malleable slug for press molds.The same metal alloy, such as Ti-6Al-4V titanium, composed of but notlimited to the constituent elements noted above, may be used for bothtypes of molds. For a sealing body including an internal reinforcementstructure 60, in some embodiments, a sand casting type mold is used andthe reinforcement structure 60 is formed in the mold for each half ofthe sealing body using the same material for the sealing body 24 and thereinforcement structure 60. In other embodiments, the reinforcementstructure 60 comprises a different material than the sealing body 24.The reinforcement structure 60 may be formed separately and affixed tothe inner surface 56 of the sealing body 24.

The heated alloy hardens into the solid state and is removed from thesand or press mold when the temperature is suitably low. The halves thusproduced are placed against one another at the wall face and may be heldtogether by a fixture to assist in joining operations. Joining the twohalves typically is performed by welding the seam such as with atungsten inert gas (TIG) electric welder, which may or may not requirethe use of suitable filler rod material at the discretion of theoperator. When the equatorial seam is completely welded, the outersurface of the sealing body is machined and polished to the desiredfinished diameter.

Thus, it is apparent that there has been provided in accordance with theembodiments of the present disclosure a sealing body for use in oil andgas well perforation operations that fully satisfies the objects, aimsand advantages set forth above. While the invention has been describedin conjunction with illustrated embodiments thereof, it is evident thatmany alternatives, modifications and variations will be apparent tothose skilled in the art in light of the foregoing description.Accordingly, it is intended to embrace all such alternatives,modifications and variations as fall within the spirit and broad scopeof the invention.

What is claimed is:
 1. A sealing body for use in well perforationoperations, the sealing body comprising: a shell defining a closedcavity; wherein the shell is comprised of a metal alloy; and whereinspecific gravity of the sealing body is less than or equal to 1, where 1is the specific gravity of water.
 2. A sealing body for use in wellperforation operations according to claim 1 wherein the metal alloy is atitanium alloy.
 3. A sealing body for use in well perforation operationsaccording to claim 2 wherein the titanium alloy is Ti-6Al-4V.
 4. Asealing body for use in well perforation operations according to claim1, wherein the shell is substantially spherical.
 5. A sealing body foruse in well perforation operations according to claim 1, furthercomprising a reinforcement structure within the cavity.
 6. A sealingbody for use in well perforation operations according to claim 5 whereinthe reinforcement structure comprises one or more pairs of ribsadjoining an inner surface of the shell.
 7. A sealing body for use inwell perforation operations according to claim 6 wherein each rib of theone or more pairs of ribs extends in a circle adjoining the innersurface of the shell and wherein, for each pair, planes of the circlesof the ribs are orthogonal.
 8. A sealing body for use in wellperforation operations according to claim 6 wherein the ribs are spacedevenly within the cavity.
 9. A sealing body for use in well perforationoperations according to claim 6 wherein each rib has a substantiallysquare cross section.
 10. A sealing body for use in well perforationoperations according to claim 9 wherein the cross section of each rib is2 mm×2 mm.
 11. A sealing body for use in well perforation operationsaccording to claim 1, wherein the shell has: an inner surface, an outersurface and an outside diameter in a range of 2.25 to 3.5 inches; athickness between the inner surface and the outer surface in a range of0.085 to 0.135 inches; wherein the metal alloy comprises a titaniumalloy; and wherein the specific gravity of the sealing body is lessthan
 1. 12. A sealing body for use in well perforation operationsaccording to claim 5, wherein the shell has an inner surface, an outersurface and an outside diameter in a range of 1.25 to 2.0 inches; athickness between the inner surface and the outer surface in a range of0.042 to 0.06 inches.
 13. A sealing body for use in well perforationoperations according to claim 5, wherein the metal alloy is a titaniumalloy.
 14. A sealing body for use in well perforation operationsaccording to claim 7 comprising one pair of ribs wherein the planes ofthe circles of the ribs intersect a center of the sealing body.
 15. Asealing body for use in well perforation operations according to claim 7wherein: the outside diameter is in the range of 1.25 to 1.5 inches; thethickness between the inner surface and the outer surface is in therange of 0.042 to 0.055 inches; and wherein the metal alloy comprises atitanium alloy.
 16. A sealing body for use in well perforationoperations according to claim 7 comprising two pairs of ribs whereineach of the four ribs are offset from a center of the sealing body. 17.A sealing body for use in well perforation operations according to claim16 comprising wherein: the outside diameter is 1.75 inches; thethickness between the inner surface and the outer surface is 0.055inches; and wherein the metal alloy comprises a titanium alloy.
 18. Asealing body for use in well perforation operations according to claim 7comprising three pairs of ribs wherein four of the six ribs are offsetfrom a center of the sealing body and wherein the planes of the circlesof the other two ribs intersect a center of the sealing body.
 19. Asealing body for use in well perforation operation according to claim 18comprising wherein: the outside diameter is 2 inches; the thicknessbetween the inner surface and the outer surface is 0.06 inches; andwherein the metal alloy comprises a titanium alloy.
 20. A sealing bodyfor use in well perforation operations according to claim 1 wherein thecavity is evacuated of gas or liquid.
 21. A sealing body for use in wellperforation operation according to claim 1 wherein the cavity is filledwith a gas or a liquid.
 22. A sealing body for use in well perforationoperations according to claim 6 wherein the one or more pairs of ribsare comprised of a titanium alloy.
 23. A sealing body for use in wellperforation operations according to claim 21 wherein the titanium alloycomprises a Ti-6Al-4V titanium.
 24. A sealing body for use in wellperforation operations according to claim 1 wherein the outer surface ofthe sealing body comprises an irregular surface.
 25. A method ofperforming well perforation operations comprising: introducing a sealingbody into a seat positioned in a well bore, the sealing body comprisinga shell defining a closed cavity, wherein the shell is comprised of ametal alloy; and wherein specific gravity of the sealing body is lessthan or equal to 1, where 1 is the specific gravity of water; andpressurizing a portion of the well bore up-hole from the seat to apredetermined pressure threshold for triggering a perforating gun.